Complex aluminum-monohydrated alkaline earth metal salt lubricant

ABSTRACT

A GREASE COMPOSITION COMPRISING A LUBRICATING OIL, A COMPLEX ALUMINUM SALT AND A MONOHYDRATED ALKALINE EARTH METAL SALT OF A C2 TO C5 FATTY ACID DISPLAYS THE PROPERTIES OF GOOD STRUCTURAL STABILITY AND EXCELLENT LOAD-CARRYING ABILITY. SPECIFICALLY A MONOHYDRATED CALCIUM ACETATE IMPARTS, TO A GREASE CONTAINING A COMPLEX ALUMINUM SALT OF ALUMINUM ALCOHOLATE, A HIGHER FATTY ACID AND AN AROMATIC ACID, STRUCTURAL STABILITY AND LOAD CARRYING PROPERTIES WHICH COULD NOT BE OBTAINED BY EMPLOYING AN AQUEOUS OR MULTIHYDRATED CALCIUM ACETATE COMPOUND.

United States Patent 3,574,111 COMPLEX ALUMINUM-MONOHYDRATED ALKA- LINE EARTH METAL SALT LUBRICANT Arnold J. Morway, Clark, N..I., assignor to Esso Research and Engineering Company No Drawing. Filed Apr. 1, 1968, Ser. No. 717,938 Int. Cl. (110m /16 US. Cl. 25236 5 Claims ABSTRACT OF THE DISCLOSURE A grease composition comprising a lubricating oil, a complex aluminum salt and a monohydrated alkaline earth metal salt of a C to C fatty acid displays the properties of good structural stability and excellent load-carrying ability. Specifically a monohydrated calcium acetate imparts, to a grease containing a complex aluminum salt of aluminum alcoholate, a higher fatty acid and an aromatic acid, structural stability and load carrying properties which could not be obtained by employing an aqueous or multihydrated calcium acetate compound.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a grease containing a complex aluminum salt which demonstrates high structural stability and good load carrying characteristics. More particularly, the invention relates to a complex aluminum soap grease which exhibits good structural stability and good load carrying properties which contains a monohydrated alkaline earth metal salt of a C to C fatty acid.

Description of the prior art Complex aluminum salt greases have long been known in the lubricating art. Such greases have been described in U.S. Patents 2,768,138 and 3,345,291 and generally in the text Lubricating Greases by C. I. Boner (Reinhold Publishing Company, New York, N.Y., 1954), pages 293- 335. These greases are characterized as having very high melting points and relatively high resistance to water solubility. Such aluminum complex greases, however, demonstrate little or no load carrying ability or structural stability. Attempts to impart load carrying ability by the use of inexpensive extreme pressure agents such as lead soap and sulfurized oils generally resulted in impairment of the structural stability of the lubricating grease, particularly at elevated temperatures. Some of these extreme pressure additives also exhibit the undesirable property of turning the grease black.

SUMMARY OF THE INVENTION It has now been found that an aluminum complex grease having excellent load carrying ability and good structural stability can be obtained by the addition to such grease of a pre-pared monohydrated alkaline earth metal salt of a C to C fatty acid. Such an aluminum complexalkaline earth metal salt grease can be described as comprising: (a) a major amount of lubricating oil; (b) about 2 to 15 wt. percent, preferably 5 to wt. percent of the reaction product of an aluminum alcoholate of the general formula:

where R is a C to C preferably C branched or straight chain alkyl group, a C to C preferably a C to C 3,574,111 Patented Apr. 6, 1971 fatty acid, and an aromatic acid having the general formula:

C O O H )n where Ar is an aromatic group and X is selected from the group consisting of hydrogen, a lower alkyl group, an amino group, a halogen and combinations thereof and n is an integer of from 1 to 5; and (c) about 10 to 25, preferably 15 to 20, wt. percent of a monohydrated alkaline earth metal salt of a C to C preferably a C fatty acid.

Suitable aluminum alcoholates for use in the preparation of the aluminum grease are those in which the alcohol precursor is ethyl alcohol, propyl alcohol, isopropyl alcohol, any of the butyl alcohols, or mixtures of the foregoing alcohols.

Suitable higher fatty acids for use in the preparation of the complexaluminum salt greases are caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, 12-hydroxy stearic acid, arachidic acid, melissic acid, oleic acid and linoleic acid. Phenyl-substituted fatty acids such as phenyl decanoic acid and naphthenic acids containing at least 12 carbon atoms may also be employed as the fatty acid reactant.

Aromatic acids suitable for use in the preparation of the basic complex aluminum grease are benzoic acid, the toluic acids, benzoic acids substituted with one or more ethyl, propyl or butyl groups, amino-substituted benzoic acids, chlorobenzoic acids and naphthoic acids. Preferably the aromatic carboxylic acid is a monocarboxylic acid.

The preparation of the complex aluminum salt is generally described in U.S. Patent 3,345,291. Essentially it comprises forming a complex aluminum salt in the presence of a base mineral oil by reacting a lower aluminum alcoholate with a mixture of a fatty acid, an aromatic carboxylic acid and water at moderate temperatures. The product of this reaction may be represented by the formula:

0 0iiR o AlO( 3Ar where Ar and R are as represented above and R (the fatty acid portion of this compound) is a C to C alkyl group. Of course it is realized that the reaction product is a myriad of components some of which are unreacted or partially reacted starting materials. It is to be emphasized, however, that the aluminum complex salt which is well known in the art as a grease component is not per se the subject of this invention but it is in combination with the monohydrated alkaline earth metal salt.

Another method of incorporating the complex aluminum salt into a lubricating oil is simply to mix the preformed salt into the oil as described in US. Patent 2,768,138.

The lubricating oils used in the compositions of the invention may be either a mineral lubricating oil or a synthetic lubricating oil. Synthetic lubricating oils which may be used include polyphenyl ether oils, polysilicone oils, esters of dibasic acids (e.g., di-2-ethylhexyl sebacate), esters of glycols (e.g., C Oxo acid diester of tetraethylene glycol), complex esters (e.g., the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethyl-hexanoic acid), halo-carbon oils, alkyl silicates, sulfite esters, mercaptals, formals, polyglycol type synthetic oils, etc. or mixtures of any of the above in any proportions.

The monohydrated alkaline earth metal salts of the C to C fatty acids which are to be added to the complex aluminum grease are the monohydrated magnesium, calcium or barium salts of acetic, propanoic, butyric or valeric acids. The preferred salt is calcium acetate monohydrate.

The preparation of the complex aluminum monohydrated alkaline earth metal salt grease of this invention generally comprises the steps of preparing an aluminum complex grease from the compounds of an aluminum alcoholate, a C to C fatty acid and aromatic carboxylic acids; adding to the aluminum complex grease a monohydrated alkaline earth metal salt of a C to C preferably C fatty acid in an amount sufficient to impart to the lubricating grease composition load carrying ability, usually about 15 to 20 wt. percent based on the total amount of the monohydrated lubricating grease and heating the mixture for a time and at a temperature sufficient to purge free water or water of hydration less stable than the monohydrate from the grease composition. Usually the composition is heated for about 3 to 5 hours at a temperature of between about 300 F. to 340 F. being careful not to fiuidize the grease.

A small amount of water is also necessary in the complex aluminum monohydrated alkaline earth metal salt lubricating composition of this invention to preserve its structural stability. Attempts to use aqueous solutions of alkaline earth metal salts or solid higher hydrates result in loss of grease structure at elevated temperature. It has been found, however, that the bound water of the monohydrated alkaline earth metal salts preserves the stability of the complex aluminum alkaline earth metal salt grease of this invention at the temperatures at which this grease is normally used. It is therefore necessary to eliminate as much free water as possible while keeping the monohydrated salt in its bound form. This is normally done by heating the grease containing the complex aluminum salt and the monohydrated alkaline earth metal salt at a temperature below about 350 -360 F. Above this point the hydrated water becomes available as free water and the structural stability of the grease is lost, thus resulting in fiuidization. In the preparation of the grease of this invention, the practice is to heat the complex aluminum monohydrated alkaline earth metal salt grease to a temperature below the dehydration temperature of the monohydrate, usually between about 300 to 340 F. for a period of time to expurge from the grease any free water or water of hydration less stable than the monohydrate, usually for about 3 to 5 hours.

'Various other additives may also be added to the lubrisuch as phenylalpha-naphthylamine, tackiness agents such as polyisobutylene, stabilizers such as aluminum hydroxy stearate, rust preventives such as sodium nitrites, etc.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will be further understood by the following example which is not to be construed as a limitation on the invention.

Example A complex aluminum base grease was prepared by charging to an electrically heated grease kettle: 6.0 parts by weight of Hydrofol acids 51, 2.6 parts by weight of benzoic acid, and 29 parts by weight of a mineral lubrieating oil having a viscosity of 510 SUS at 100 F. The contents of the kettle were heated wihile mixing to 200 F. and held at that temperature for 30 minutes. Hydrofol acids 51 is a commercial acid obtained by hydrogenating fish oil and has an average chain length and degree of unsaturation corresponding to stearic acid. 4.4 parts by weight aluminum isopropoxide and 29' parts by weight of the lubricating oil were charged to a separate fireheated kettle and heated to 220 F. for 30 minutes until a clear solution appeared. The mixture of the Hydrofol acids, benzoic acid, and oil was then charged to the kettle containing the aluminum isopropoxide and the entire contents were heated, while mixing, to 300 F. for 40 minutes. This mixture was then cooled to 200 F. at which point 16 ml. of water was added. The batch was then reheated to 290 F. at which point 2 9 parts by weight of the mineral oil was added. The batch was then heated to 400-410 F. and held at that temperature for one hour. This complex aluminum grease product was cooled to 300 F. at which point 64.3 parts by weight were removed and Morehouse milled.

To the remainder of the aluminum base grease were added at 300 F. 17.9 parts by weight of calcium acetate monohydrate in a dry powder form. and 45.7 parts by weight of mineral oil. This grease product was held at 315 -325 F. for 3 hours to purge out any free water or water of hydration less stable than the monohydrate. The grease was then cooled to F. and Morehouse milled.

The grease containing the monohydrated calcium acetate, designated as Grease I, was compared with a complex aluminum grease base, designated as Grease A, and with a. similar grease containing calcium acetate dihydrate Ca (C H O -2H O, designated as Grease -B, in the following table.

Composition (weight percent):

Hydrotol Acids 51 Benzoic acid Aluminum isopropoxide Calcium acetate monohydrate Calcium acetate dihydrate Phenyl-a-naphthylamine .71 0.71. Mineral oil 76.77. 94.63- 76.77. Properties:

Appearance Excellent, smooth--- Excellent, smooth.-- Dropping point, F 386-400 400+ Fluidizes at 250 F. 400 F. beaker test:

Consistency F Like original Like original Consistency 200 F. do do Consistency 300 F Soft but excellent Soft but excellent structure. structure. Consistency 360 F Very soft-approaoh- Semi-fluid ing semi-fiuid. Consistency 400 F Viscous product Fluid, sloppy structure. Cooling to 80 F Like original Not reversible,

sloppy structure.

Timken Load Test:

40 lbs Pass Pass 1 20 lbs Fail 1 Sometimes passes, sometimes fails, marginal.

eating composition (e.g., 0.1 to 10.0 wt. percent each, based on the total weight of the composition). Specfiic The 400 F. Beaker Test consists of slowly heating the grease to 400 F. while stirring slowly and observing examples of these additives include oxidation inhibitors 75 changes, if any, in the consistency of the grease at various intermediate temperatures. It will be noted from the table that the consistency of the grease containing the monohydrated calcium acetate remained like the original grease to temperatures of about 360 F. at which point it began to turn fluid. This was also the case with the complex aluminum base grease except that, upon cooling, the grease containing the calcium salt returned to a solid state with consistency like the original unheated grease whereas the base grease remained semi-fluid on cooling indicating poor structural stability to heating. It is also to be noted that the grease containing calcium acetate dihydrate fluidized at 250 F. Fluidizing at this temperature indicated not only poor structural stability 'but an undesirably low dropping point.

The Tim ken Load Test is a means of measuring the ability of a lubricant to function under extreme pressure without causing sliding surfaces to become scarred or welded. In this test a lubricant film is maintained between a rotating cup and a stationary block. Pressure between the cup and block is created by weights on a lever arm. Pressure is increased on the lever arm until the grease fails, causing a scarring or welding of the cup and block. The greater the pressure the lubricant can withstand without failing, the better its load carrying characteristics. It can be seen from the table that the grease containing the monohydrated calcium acetate was able to pass a much greater load than was the grease without this ingredient. It can also be seen that a grease containing dihydrated calcium acetate did not have the load carrying characteristics of a grease containing the monohydrated salt.

What is claimed is:

1. A complex aluminum salt alkaline earth metal salt lubricating grease composition which comprises:

(a) a major amount of lubricating oil;

(b) about 2 to 15 wt. percent of a complex aluminum salt; and

(c) about to 25 wt. percent of a monohydrated alkaline earth metal salt of a C to C fatty acid;

said weight percents being based on the total composition; said complex aluminum salt being represented by the formula:

O 0- i l-R where R is a C to C alkyl group, R is a C to C alkyl group, and Ar is an aromatic group.

2. A lubricating composition as in claim 1 wherein the monohydrated alkaline earth metal salt is calcium acetate monohydrate.

3. A lubricating composition as in claim 1 wherein the lubricating oil is a mineral lubricating oil.

4. A lubricating composition as in claim 2 wherein the complex aluminum salt forms about 5 to 10 wt. percent of the total lubricating composition and the calcium acetate monohydrate forms about 15 to 20 wt. percent of the total lubricaing composition.

5. A lubricating composition as in claim 1 wherein R is an isopropyl group, Ar is a benzyl group and R is a stearic group.

References Cited UNITED STATES PATENTS 2,583,394 1/1952 Schott et al. 252-36 2,768,138 10/1956 Hotten et al 252-377 2,846,392 8/1958 Morway et a1 2S236 2,927,892 3/ 1960 Morway 252-39 2,976,242 3/ 1961 Morway 252-36 OTHER REFERENCES Advances in Petroleum Chemistry and Refining, by Kobe et al., Interscience Pub., 1964, vol. 9, New York, p. 128.

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner U.S. Cl. X.R. 252-17, 37.7 

